A diver explored the wreck, lying under 100ft of water off the port of Ostend.

It is the 11th German submarine from the 1914-18 war to be found in Belgian waters and the best-preserved example to date, Thomas Termote, a diver and expert in marine archaeology who found the wreck this summer.

‘We thought that all the big wrecks had already been discovered so this was a total surprise,’ Termote said.

Its exact location is being kept secret to deter treasure-hunters.

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It is the 11th submarine from the 1914-18 war to have been found in Belgian waters (Picture: Tomas Termote)

He said the wreck – a UB-II type torpedo armed boat – was 88ft long long with the rear end partly detached.

‘The submarine is very intact, everything is still closed – that’s what he (Termote) saw during his first visit this summer,’ Jan Mees, head of the Flanders Marine Institute said.